Suspension device

ABSTRACT

A suspension device (S) comprises: an actuator (A) including a motion conversion mechanism (T) for converting rotational motion of a screw nut ( 1 ) to linear motion of a threaded shaft ( 2 ), and a motor (M) connected to the screw nut ( 1 ); and a fluid pressure damper (D) connected to the threaded shaft ( 2 ), wherein the threaded shaft ( 2 ) is formed in a cylindrical shape, a connecting shaft ( 30 ) for connecting a rod ( 31 ) or a cylinder ( 32 ) of the fluid pressure damper (D) to the threaded shaft ( 2 ) is inserted into the threaded shaft ( 2 ), and the connecting shaft ( 30 ) is connected to an end, opposite to the fluid pressure damper, of the threaded shaft ( 2 ). Accordingly, the connection between the actuator and the hydraulic damper is facilitated.

FIELD OF THE INVENTION

The present invention relates to an improved suspension device forsuppressing relative movement between a vehicle body and an axle by anelectromagnetic force generated in a motor.

DESCRIPTION OF THE RELATED ART

As this kind of suspension device, as disclosed in Japanese PatentApplication Laid-Open No. 2001-180244, a suspension device comprising ahydraulic damper and an actuator for providing a thrust to a piston rodof the hydraulic damper is proposed. In this device, a rod of thehydraulic damper is formed in a cylindrical shape with an internalthread part being provided on the inner circumferential side of the rod,and a shaft having one end connected to a rotor of a motor and the otherend connected to an external thread member to be screwed to the internalthread part of the rod is inserted to the rod of the hydraulic damper,whereby the piston rod of the hydraulic damper is constituted by theabove-mentioned shaft and rod.

This proposal intends to damp vibration by adding, to a damping forcegenerated by the hydraulic damper, a force which is generated whenrelatively moving the shaft and the rod in the axial direction by amotor to extend/contract the piston rod, or by converting a torque ofthe motor to a force in the relative movement direction of the shaft andthe rod to thereby additively act this force on the damping force of thehydraulic damper.

Another suspension device is also disclosed in Japanese PatentApplication Laid-Open No. 08-197931, the suspension device comprising: acoil spring for elastically supporting a vehicle body side or a sprungmember side of a vehicle; an actuator including a threaded shaftrotatably screwed to a ball screw nut connected to an axle or anunsprung member side, and a motor interposed between a pair of springswhile being connected to one end of the threaded shaft and elasticallysupported on the sprung member side; and a hydraulic damper fixed to thevehicle body side to damp vertical vibration of the actuator, in whichthe relative movement between the vehicle body and the axle is activelycontrolled by the thrust of the actuator.

DISCLOSURE OF THE INVENTION

The above-mentioned conventional suspension devices are problematic inthe following point.

In the conventional suspension devices in which the hydraulic damper isserially connected to the actuator as described above, since thehydraulic damper that is a heavy product must be connected to theactuator at a connecting part located at the middle of the suspensiondevice in assembling of the hydraulic damper and the actuator, theassembling operation is troublesome, and worker's burden is alsoincreased.

In view of the above-mentioned defect, the present invention provides asuspension device in which connection between an actuator and ahydraulic damper is facilitated.

To attain the above-mentioned object, a suspension device according tothe present invention comprises: an actuator including a motionconversion mechanism for converting rotational motion of a screw nut tolinear motion of a threaded shaft, and a motor connected to the screwnut; and a fluid pressure damper connected to the threaded shaft, inwhich the threaded shaft is formed in a cylindrical shape, a connectingshaft for connecting a rod or a cylinder of the fluid pressure damper tothe threaded shaft is inserted into the threaded shaft, and theconnecting shaft is connected to an end, opposite to the fluid pressuredamper, of the threaded shaft.

According to the suspension device of the present invention, in anassembling process for integrating the fluid pressure damper to theactuator, the fluid pressure damper that is a heavy product can beintegrated to the actuator not by the connecting operation at the middleof the fluid pressure damper and the actuator, but only by an operationfrom the side opposite to the fluid pressure damper. Therefore, theconnecting operation of the fluid pressure damper to the actuator isfacilitated, and the worker's burden can be also remarkably reduced.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical sectional view of a suspension device according toa preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be then described based on a preferredembodiment shown in the drawing.

A suspension device S according to one preferred embodiment of thepresent invention, as shown in FIG. 1, basically comprises: an actuatorA including a motion conversion mechanism T for converting rotationalmotion of a ball screw nut 1 that is a screw nut to linear motion of athreaded shaft 2, and a motor M connected to the ball screw nut 1; and afluid pressure damper D connected to the threaded shaft 2.

This suspension device S can function as an actuator since the threadedshaft 2 can be linearly moved in the vertical direction in FIG. 1 bydriving and rotating the ball screw nut 1 by the torque generated by themotor M.

When the threaded shaft 2 is forcedly linearly moved by an externalforce, a rotor R of the motor M performs rotational motion, while themotor M works to generate a torque for suppressing the rotational motionof the rotor R resulting from induction electromotive force to suppressthe linear motion of the threaded shaft 2. That is, in this case, thelinear motion in the vertical direction in FIG. 1 of the threaded shaft2 that is a linear motion side member is suppressed by a regenerativetorque that the motor M generates by regeneratively converting anexternally input kinematic energy into an electric energy.

That is, this suspension device S can provide a thrust to the threadedshaft 2 by causing the motor M to actively generate the torque, and alsocan suppress the linear motion of the threaded shaft 2, when thethreaded shaft 2 is forcedly moved by external force, by theregenerative torque generated by the motor M.

Accordingly, this suspension device S can simultaneously perform, forexample, attitude control of a vehicle body of a vehicle, when used bybeing interposed between the vehicle body and axle of the vehicle, sinceit not only simply generates the damping force for suppressing thelinear motion of the threaded shaft 2 but also works as the actuator.Thus, this suspension device S can function also as an activesuspension.

In this suspension device S, the fluid pressure damper D is seriallyconnected to the threaded shaft 2, and this fluid pressure damper D isprovided mainly for the purpose of absorbing high frequency vibration.That is, the fluid pressure damper D absorbs, upon input of highfrequency vibration such as a vibration with relatively largeacceleration, its vibration energy by being serially connected to theactuator A large in moment of inertia which is difficult toextend/contract, in response to input of high frequency vibration, andeasy to transmit the vibration.

The suspension device S can effectively perform vibration suppression,upon input of not only low frequency vibration but also high frequencyvibration by running on a projection on road, to improve the vehicleride quality.

For details, the threaded shaft 2 is formed in a cylindrical shape asshown in FIG. 1, and includes a spiral thread groove (not shown), whichis formed on the outer circumference thereof; and a linear spline groove(not shown), which is formed along its axial line, namely, the linearmotion direction of the threaded shaft 2. To prevent the threaded shaft2 from dropping out of a ball spline nut 3 to be hereinafter described,the spline groove does not have to be formed at both terminal ends ofthe threaded shaft 2, and the number of spline groove to be provided canbe optionally set.

On the other hand, the ball screw nut 1 is not shown in detail as it iswell-known, but includes a spiral passage provided on the innercircumference of a cylindrical body to face the thread groove of thethreaded shaft 2; a circulation path provided within the cylindricalbody to communicate both ends of the above-mentioned passage with eachother; a plurality of balls housed in the passage and circulation pathand traveling along the thread groove; and a spacer interposed eachbetween the balls, in which each ball can circulate in the loopedpassage and circulation path. Although smooth linear motion of thethreaded shaft 2 is attained by using the ball screw nut 1 as a screwnut in this embodiment, a nut simply including a screw thread screwed tothe thread groove of the threaded shaft 2 may be also adopted. Anannular groove 1 a is provided on the outer circumference of the ballscrew nut 1, and a cylindrical socket 1 b is provided at the upper endthereof in FIG. 1.

A locking mechanism of the threaded shaft 2 is required to linearly movethe threaded shaft 2 by the rotary drive of the ball screw nut 1. Inthis embodiment, the locking mechanism is constituted by the splinegroove provided on the outer circumference of the threaded shaft 2 andthe ball spline nut 3. The ball spline nut 3 is not shown in detailsince it is well-known, but includes a linear passage provided on theinner circumference of a cylindrical body to face the spline grooveprovided on the outer circumference of the threaded shaft 2; acirculation path provided within the cylindrical body to communicateboth ends of the passage with each other; a plurality of balls housed inthe passage and circulation path and traveling along the spline groove;and a spacer interposed each between the balls, in which each ball cancirculate in the above-mentioned looped passage and circulation path. Akey groove 3 a is provided on the lateral of the ball spline nut 3.

The ball screw nut 1 is screwed to the threaded shaft 2 along the threadgroove, and the ball spline nut 3 is inserted to the threaded shaft 2along the spline groove.

Both the ball screw nut 1 and the ball spline nut 3 are retained by theinner circumference of a cylindrical holder 5 with the ball screw nut 1being up in FIG. 1.

The holder 5 is formed in a cylindrical shape, and includes a pluralityof nut parts 5 a with screw hole, each provided to protrude toward theupper end outer circumference in FIG. 1; a flange 5 b protrudinginwardly from the lower end inner circumference in FIG. 1; a steppedpart 5 c provided at the middle of the inner circumference; aninstallation part 5 d for installing a rubber vibration isolator 21,which is composed of a pair of annular projections provided at themiddle of the outer circumference; and a key groove 5 e provided in theinner circumference below the stepped part 5 c in FIG. 1.

The ball spline nut 3 is fitted to the inner circumference of the holder5 below the stepped part 5 c, and retained in the holder 5 in a lockedstate by a key 6 inserted to the key groove 3 a provided in the outercircumference of the ball spline nut 3 and to the key groove 5 eprovided in the inner circumference of the holder 5.

The ball spline nut 3 is held between a snap ring 7 attached to theinner circumference of the holder 5 and the flange part 5 b of theholder 5 while abutting on the upper end in FIG. 1 of the ball splinenut 3, and is prevented from dropping out of the holder 5.

The ball screw nut 1 is rotatably retained by the holder 5 through aball bearing 9 which is fixed to the inner circumference of the holder 5while being held between the stepped part 5 c provided on the innercircumference of the holder 5 and a nut 8 screwed to the innercircumference of the holder 5. A ball 9 a of the ball bearing 9 travelsalong an annular groove 1 a formed in the outer circumference of theball screw nut 1, and the ball screw nut 1 can be fixed to the holder 5by causing the ball screw nut 1 itself to work as an inner ring of theball bearing 9, and fixing an outer ring 9 b of the ball bearing 9 tothe holder 5. The ball screw nut 1 and the ball spline nut 3 arearranged adjacently to each other while being retained by the holder 5.

That is, the motion conversion mechanism T composed of the ball screwnut 1 and the threaded shaft 2 is retained by the holder 5 as anassembly with the threaded shaft 2 being locked, and when the ball screwnut 1 performs rotational motion, the threaded shaft 2 is locked by theball spline nut 3, whereby the threaded shaft 2 performs linear motionin the vertical direction in FIG. 1.

In this embodiment, since the ball screw nut 1 and the threaded shaft 2in the motion conversion mechanism T and further the ball spline nut 3as the locking mechanism of the threaded shaft 2 are made into anassembly, as described above, with the threaded shaft 2 and the ballscrew nut 1 being axially aligned by holding these members by one holder5, the operation of the motion conversion mechanism T is assured.

Accordingly, since the motor M is fixed to the holder 5 with the shaft17 of the motor M being axially aligned to the threaded shaft 2 and theball screw nut 1 by the holder 5, the thread groove of the threadedshaft 2 and the ball as the screw thread of the ball screw nut 1 arenever loaded, or no radial bias load acts on the shaft 17 of the motorM. Consequently, reduction in life of the actuator A or deterioration ofdurability of the suspension device S is never caused.

Further, since the shaft 17 of the motor M is axially aligned to thethreaded shaft 2 and the ball screw nut 1 by the holder 5, thesuspension device S can be mounted on a vehicle without axial alignmentoperation between the threaded shaft 2 and the ball screw nut 1, and themounting operation on the vehicle is thus remarkably facilitated,compared with the conventional suspension device.

Further, since the assembling of the actuator A is completed by makingthe threaded shaft 2 and the ball screw nut 1 into an assembly by theholder 5 and connecting the motor M to this assembly, the assemblingprocess in the part of the actuator A of the suspension device S is alsofacilitated.

That is, the above-mentioned integral retainment of all components ofthe motion conversion mechanism T by the holder 5 has the followingadvantages: the connection of the motor M to the motion conversionmechanism T can be performed without the operation of rotating the ballscrew nut 1 to pull the threaded shaft 2 into the motor M, which isrequired when adopting a structure such that a member which performsrotational motion of the motion conversion mechanism T or the ball screwnut 1 in this case is not retained by the holder 5 but incorporated tothe motor M side, and further without consideration for locking betweenholders, which is required when adopting, instead of the incorporationof the ball screw nut 1 to the motor M, a structure such that the ballscrew nut 1, the threaded shaft 2 and the ball spline nut 3 are retainedrespectively by different holders.

The above-mentioned advantages of retaining the ball screw nut 1, thethreaded shaft 2 and the ball spline nut 3 by one holder 5 neverprecludes adoption of the structure such that the ball screw nut 1, thethreaded shaft 2 and the ball spline nut 3 are retained respectively bydifferent holders.

The length of the threaded shaft 2 located in a section between the ballscrew nut 1 used to axially drive the threaded shaft 2 and the ballspline nut 3 that is a component of the locking mechanism of thethreaded shaft 2 can be reduced by arranging the ball screw nut 1 andthe ball spline nut 3 adjacently to each other.

The part located in the above-mentioned section of the threaded shaft 2is to be twisted by the rotary drive of the ball screw nut 1, and theshorter the section is, the shorter the part to be twisted is.

Since the threaded shaft 2 works also as a spring element by beingtwisted, it takes longer time for the linear motion of the threadedshaft 2 to respond to the rotation of the ball screw nut 1 as thesection to be twisted is longer. However, since the section to betwisted of the threaded shaft 2 can be reduced by arranging the ballscrew nut 1 and the ball spline nut 3 adjacently to each other asdescribed above, the responsiveness of the suspension device S, whenfunctioning as the actuator, is improved.

The improved responsiveness of the suspension device S when functioningas the actuator leads to improved controllability when activelycontrolling the vehicle attitude.

On the other hand, the motor M includes, as shown in FIG. 1, a toppedcylindrical casing 10; a stator 11 fixed to the inner circumference ofthe casing 10, the stator including a core 11 a that is an armature ironcore and a coil 11 b wound around the core 11 a; an annular cap 12fitted to the lower end opening in FIG. 1 of the casing 10; acylindrical sensor holder 13 housed in and fixed to the top side innercircumference of the casing 10, the holder retaining a resolver stator13 on its inner circumference; and a rotor 16 rotatably housed in thecasing 10 through a ball bearing 14 fixed to the inner circumference ofthe sensor holder 13 and a ball bearing 15 fixed to the innercircumference of the cap 12. The cap 12 includes a cylindrical part 12 afitted to the inner circumference of the casing 10; a collar part 12 bprovided on the outer circumference of the cylindrical part 12 a to abuton a flange 10 a provided on the lower end outer circumference in FIG. 1of the casing 10; and a cylindrical fitting part 12 c suspended from thecylindrical part 12 a and fitted to the upper end inner circumference ofthe holder 5.

The rotor 16 includes a cylindrical shaft 17, and a magnet 18 attachedto the middle outer circumference of the shaft 17 so as to face the core11 a, and the shaft 17 is rotatably housed in the casing 10 with itsupper end being pivotally supported by the inner circumference of theball bearing 14 and its lower end being pivotally supported by the innercircumference of the ball bearing 15. Although the magnet 18 is formedin an annular shape by adhering a plurality of magnets so that N-poleand S-pole are alternated along the circumference, an annular magnethaving a split pole pattern in which N-pole and S-pole are alternatedalong the circumference can be also used.

Accordingly, various types can be used as the motor M, in addition tothe structure as a brushless motor in this embodiment, and concreteexamples thereof include DC motor, AC motor, induction motor, andsynchronous motor.

A resolver core 13 b is attached in a position facing the resolverstator 13 a fixed to the inner circumference of the sensor holder 13 onthe upper end outer circumference of the shaft 17 in the rotor 16, sothat a rotational position of the rotor 16 can be detected by theresolver stator 13 a and resolver core 13 b. Thus, the motor M can becontrolled based on the rotational position or rotating speed of therotor 16 by a control device (not shown) which controls current-carryingto the coil 11 b. As a means for performing position detection of therotor 16, a magnetic sensor such as a Hall element, a rotary encoder orthe like can be adopted in addition to the above-mentioned resolver.

Although it is a matter of course that the ball bearing 14 and theresolver stator 13 b can be directly fixed to the casing 10 withoutthrough the sensor holder 13, the use of the sensor holder 13 offers anadvantage that the ball bearing 14 and the resolver stator 13 b can befixed within the casing 10 without special processing to the casing 10.

The thus-constituted motor M is thread-fastened and mounted on the upperend in FIG. 1 of the holder 5 by a bolt 19. For details, the motor M isfixed to the upper end of the holder 5 by screwing the bolt 19 insertedthrough the flange 10 a of the casing 10 and the collar part 12 b of thecap 12 to the nut part 5 a provided on the upper end outer circumferenceof the holder 5.

When the motor M is integrated to the holder 5, the shaft 17 of themotor M is connected to the ball screw nut 1 by inserting the lower endof the shaft 17 to the inner circumference of a socket 1 b of the ballscrew nut 1, so that the threaded shaft 2 can be linearly moved in thevertical direction in FIG. 1 by driving and rotating the ball screw nut1 by the motor M. Thus, the motor M can be connected to the motionconversion mechanism T only by fixing the motor M to the holder 5 toassemble the actuator A.

A tolerance ring 20 is interposed between the outer circumference of theshaft 17 and the inner circumference of the socket 1 b, and thetolerance ring 20 works as a torque limiter for regulating the upperlimit of relative rotary torque around an axis which acts on the shaft17 and the ball screw nut 1.

For details, the tolerance ring 20, which is formed in an annular shapeby use of a corrugated sheet material, works as the torque limiter inthe following manner. The tolerance ring 20 exhibits an energizingforce, when interposed between the shaft 17 and the socket 1 b, as areaction of radial compression of corrugations formed on the sheetmaterial, and according to the energizing force, a friction forceagainst the relative rotation of the shaft 17 and the socket 1 b iscaused between the tolerance ring 20 and the shaft 17 and socket 1 b, inwhich the shaft 17 and the ball screw nut 1 are integrated togetherwithout relative rotation until a relative torque causing the relativerotation exceeds the friction force, while the shaft 17 and the ballscrew nut 1 are relatively rotated when the relative torque exceeds themaximum friction force.

In the suspension device S of this embodiment which is adapted tosuppress relative vibration between a sprung member and an unsprungmember of a vehicle, when an external force such that it suddenlyextends/contracts the suspension device S is input, the linear motion ofthe threaded shaft 2 is increasingly accelerated to excessively increasethe torque for rotating the ball screw nut 1, and the relative torquefor relatively rotating the shaft 17 and the ball screw nut 1 exceeds afriction force resulting from the energizing force of the tolerance ring20, causing spin of the ball screw nut 1 to the shaft 17. Then, only theball screw nut 1 is rotated without rotation of the shaft 17, and thetransmission of the torque generated in the motor M based on the momentof inertia or electromagnetic force to the ball screw nut 1 is thussuppressed.

In a situation as described above, or when the speed of stroke of thesuspension device S is largely changed, accordingly, since thetransmission of the torque generated in the motor M to the ball screwnut 1 is, suppressed to prevent a torque more than a relative torquepermitted according to the energizing force of the tolerance ring 20from acting on the ball screw nut 1, the effect of the moment of inertiaof the motor M can be reduced to prevent the generated damping force ofthe suspension device S from being excessive, and transmission of asudden vibration inputted to the unsprung member to the sprung membercan be consequently suppressed.

Although the tolerance ring 20 is used as the torque limiter in theabove, a friction body which causes the shaft 17 and the socket 1 bgenerate a friction force can be interposed instead. As the frictionbody, for example, an annular rubber or an annular plate with roughsurface can be adopted.

The relative torque adjusted by the tolerance ring 20 or the frictionbody can be set to an experimentally or empirically-obtained value sothat the effect of the moment of inertia caused when passing over aprojection or groove on road can be reduced, although it can beoptionally adjusted according to a control object to which thesuspension device S is applied.

In the suspension device S of this embodiment, since the effect of themoment of inertia in which the generated damping force becomes excessivedue to superimposition of the moment of inertia of the motor M on thetorque resulting from the electromagnetic force of the motor M can bereduced, the vehicle ride quality can be improved.

In other words, the motion conversion mechanism T is immune to breakageby an effect of excessive torque since a torque exceeding an allowablerelative torque does not act on the ball screw nut 1, and flying of themagnet 18 fixed around the rotor 16 can be also prevented to reduce theload on the motor M since a large angular acceleration can be preventedfrom acting on the rotor 16 of the motor M. Thus, the reliability of thesuspension device S is improved.

Further, according to the suspension device S of this embodiment, thestroke length can be easily ensured since the tolerance ring 20 as thetorque limiter is interposed to the fitting part between the cylindricalshaft 17 of the motor M and the socket 1 b of the ball screw nut 1 witha minimal effect on the whole length of the suspension device S, or thetorque limiter is provided in a position never affecting the strokelength.

Although the shaft 17 is connected to the ball screw nut 1 through thetolerance ring 20 in this embodiment, the ball screw nut 1 may bedirectly attached to the shaft 17 of the rotor 16 if it is not needed toprovide the torque limiter, or the magnet 18 may be attached to theouter circumference of the ball screw nut 1 by using the ball screw nut1 itself as a shaft in the rotor 16 of the motor M. The idea ofconnecting the ball screw nut 1 to the motor M in this embodiment has anintent that whether direct connection or indirect connection isregardless, and the idea includes also use of the ball screw nut 1itself as the rotor 16. When the ball screw nut 1 is directly attachedto the shaft 17 of the rotor 16, a spline or key can be used as astopper, and a structure in which the ball screw nut 1 is fitted to theinner circumference of the shaft 17 can be also adopted.

The thus-constituted actuator A is connected to a mount 22 through therubber vibration isolator 21 installed to the installation part 5 d onthe outer circumference of the holder 5. Concretely, the mount 22includes a mount cylinder 23; an annular plate 24 connected to a sprungmember (not shown) of a vehicle; and a rubber pad 25 connecting themount cylinder 23 to the plate 24, and the lower end inner circumferencein FIG. 1 of the mount cylinder 23 is joined to the outer circumferenceof an embracing ring 26 which embraces the outer circumference of therubber vibration isolator 21 installed to the outer circumference of theholder 5. The embracing ring 26 includes a U-shaped sectional embracingring body 26 a which embraces the rubber vibration isolator 21, and acylindrical socket part 26 b suspended from the lower end innercircumference in FIG. 1 of the embracing ring body 26 a, and a springreceiver 43 is installed to the socket part 26 b.

Thus, the actuator A is connected to the sprung member of the vehiclethrough the mount 22 by connecting the actuator A to the mount 22.

An outer cylinder 27 is joined to the outer circumference of theembracing ring 26 for embracing the rubber vibration isolator 21, and anannular and L-shaped sectional end cap 29 is screwed to the lower end inFIG. 1 of the outer cylinder 27 to support the lower end of an annularcushion 28 fitted to the lower end inner circumference of the outercylinder 27.

Further, in this suspension device S, the threaded shaft 2 is seriallyconnected to a rod 31 of the fluid pressure damper D through aconnecting shaft 30 as shown in FIG. 1. The fluid pressure damper D isnot shown in detail since it is well-known, but includes a cylinder 32;a piston (not shown), which is slidably inserted into the cylinder 32 todefine two pressure chambers (not shown) within the cylinder 32; a rod31 protruded out of the cylinder 32 with one end thereof being connectedto the piston; and an air chamber or reservoir (not shown), which isformed within the cylinder 32 to compensate the volume of the rodprotruded to and retreated from the cylinder 32, and the fluid pressuredamper D exhibits a predetermined damping force duringextending/contracting operation.

The fluid pressure damper D may be of a single cylinder type providedwith air chambers within the cylinder 32 or a so-called double-cylindertype provided with an annular reservoir. The adoption of thedouble-cylinder type as the fluid pressure damper D has an advantagethat the whole length of the suspension device S can be reduced byreducing the whole length of the fluid pressure damper D. An annularcushion 40 is provided on the upper end outer circumference of the rod31. The annular cushion 40 butts on the upper end in FIG. 1 of thecylinder 32, when the fluid pressure damper D is contracted to themaximum, to reduce the impact in the maximum contraction.

In this suspension device S, the connecting shaft 30 is extended fromthe upper end of the rod 31 of the fluid pressure damper D, and theconnecting shaft 30 includes a tapered part 30 a that is an engagementpart to be engaged with the fluid pressure damper-side end of thethreaded shaft 2, the tapered part being formed by expanding thediameter of the lower end in FIG. 1 that is a base end connected to theupper end of the rod 31; and a thread part 30 b formed at the upper endin FIG. 1 that is a leading end. Although the rod 31 and the connectingshaft 30 are molded as an integrated unit in this embodiment, the rod 31and the connecting shaft 30 may be formed as separate members, and thenconnected to each other. Further, although the rod 31 is connected tothe threaded shaft 2 by the connecting shaft 30 in this embodiment, aninverted type can be also adopted as the fluid pressure damper D toconnect the cylinder 32 to the threaded shaft 2 by the connecting shaft30.

An annular disk 33 to be fitted to the lower end of the threaded shaft 2is installed to the outer circumference of the tapered part 30 a of theconnecting shaft 30, and a spring receiver 34 which works also as abearing in the extending/contracting direction of the suspension deviceS in slidable contact with the inner circumference of the outer cylinder27 is installed to the outer circumference of the disk 33. An annularbump cushion 41 is installed to the lower end outer circumference inFIG. 1 of the threaded shaft 2. The bump cushion 41 is restricted frommoving downwardly by the disk 33, and butts on the lower end of theholder 5, when the actuator A is contracted to the maximum, to regulatethe maximum contraction stroke length of the actuator A.

The maximum contraction stroke length of the suspension device S is thusregulated by the cushion 40 and the bump cushion 41, the cushion 40regulating the maximum contraction stroke length of the fluid pressuredamper D, and the bump cushion 41 regulating the maximum contractionstroke length of the actuator A.

The connecting shaft 30 is connected to the threaded shaft 2 byinserting the connecting shaft 30 into the threaded shaft 2, andscrewing a nut 35 to the thread part 30 b at the top end opposite to thefluid pressure damper D side. In this case, namely, the connecting shaft30 is connected to the threaded shaft 2 by holding the threaded shaft 2together with the disk 33 between the tapered part 30 a of theconnecting shaft 30 and the nut 35. The connecting shaft 30 can beaccordingly connected to the threaded shaft 2 from the side opposite tothe fluid pressure damper.

That is, in an assembling process for integrating the fluid pressuredamper D to the actuator A, the fluid pressure damper D that is a heavymatter can be integrated to the actuator A not by connecting operationat the middle of the fluid pressure damper D and the actuator A, butonly by operation from the upper side in FIG. 1 that corresponds to theside opposite to the fluid pressure damper. Therefore, the connectingoperation of the fluid pressure damper D to the actuator A isfacilitated, and the worker's burden can be also remarkably reduced.

The engagement of the engagement part of the connecting shaft 30, or thetapered part 30 a in this case, with the fluid pressure damper side endpart of the threaded shaft 2 includes, in addition to regulation of theupward movement in FIG. 1 of the connecting shaft 30 relative to thethreaded shaft 2 by direct contact of the engagement part to the fluidpressure damper-side end part of the threaded shaft 2, regulation of theupward movement in FIG. 1 of the connecting shaft 30 relative to thethreaded shaft 2 by interposition of a member such as the disk 33between the fluid pressure damper-side end part of the threaded shaft 2and the engagement part as described above. Although the shape of theengagement part is not limited to the tapered part 30 a as long as theupward movement in FIG. 1 of the connecting shaft 30 relative to thethreaded shaft 2 can be regulated, the adoption of the tapered part 30 ahas an advantage that the fastening and centering of the disk 33 to thethreaded shaft 2 are facilitated. Even if a backlash occurs between thedisk 33 and the threaded shaft 2, axial slippage of the spring receiver34, which works as the bearing, relative to the threaded shaft 2 can beprevented by the upward fastening in FIG. 1 by the tapered part 30 a,and smooth extension/contraction of the suspension device S can bemaintained.

Further, in this embodiment, a collared cylindrical spacer 36 forcentering the upper end of the connecting shaft 30 relative to thethreaded shaft 2 is fitted to the upper opening of the threaded shaft 2,and the inner circumference of the spacer 36 slidably contacts with theouter circumference of the connecting shaft 30 to arrest shaking in thecentering of the upper end of the connecting shaft 30 to the threadedshaft 2, whereby the connecting shaft 30 is prevented from interferingwith the threaded shaft 2 when vibration is input. Since the shaking ofthe connecting shaft 30 can be prevented by the spacer 36, the looseningof the nut 35 in the input of vibration is also suppressed.

The connecting shaft 30 is set long since it is inserted into thethreaded shaft 2 and connected to the threaded shaft 2 from the sideopposite to the fluid pressure damper of the threaded shaft 2 asdescribed above. Thus, the connecting shaft 30 itself can act as alongitudinal spring element to the threaded shaft 2 which moves in thevertical direction in FIG. 1 to suppress the rupture of the shaft or theloosening of the nut 35.

Additionally, since the threaded shaft 2 and the connecting shaft 30 aredetachably thread-fastened in this case, only the fluid pressure damperD or only the motion conversion mechanism T of the components of thesuspension device S can be easily replaced when required, and also canbe disassembled to inspect only a failure point. Although the detachableconnection of the threaded shaft 2 to the connecting shaft 30facilitates the maintenance of the suspension device S and the componentreplacement thereof, stationary connection of the threaded shaft 2 tothe connecting shaft 30 by welding, brazing or the like can be alsobasically adopted. This connection has no merit in the point ofmaintenance or component replacement, but has the same effect as thedetachable connection of the threaded shaft 2 to the connecting shaft 30in the point of facilitating the assembling of the fluid pressure damperD to the actuator A. That is, the connection of the threaded shaft 2 tothe connecting shaft 30 includes not only the detachable connection butalso fixation without schedule of detachment. The detachable connectioncan be performed by a method other than the thread fastening.

A cover cylinder 37 is provided on the lateral outer circumference ofthe cylinder 32 of the fluid pressure damper D to cover the cylinder 32while forming an annular clearance from the cylinder 32, and the upperend of the cover cylinder 37 is folded to form a collar part 37 a.

The collar part 37 a of the cover cylinder 37 butts on a cushion 28fitted to the lower end inner circumference in FIG. 1 of the outercylinder 27 when the suspension device S is extended to the maximum, andthe cushion 28 regulates the overall full extension of the suspensiondevice S.

Since the fluid pressure damper D and the actuator A independentlyextend and contract, the overall maximum extension stroke length of thesuspension device S reaches the total of maximum extension strokelengths of the fluid pressure damper D and the actuator A without suchregulation. Therefore, the overall maximum extension stroke length ofthe suspension device S is regulated by the collar part 37 a and thecushion 28.

An annular spring receiver 42 is placed on the bottom of the covercylinder 37 and housed in the lower end inner circumference of the covercylinder 37. A spring 38 to be juxtaposed to the fluid pressure damper Dis interposed between the spring receiver 42 and the lower end of thespring receiver 34, and a spring 39 to be juxtaposed to the actuator Ais interposed between the spring receiver 43 installed to the socketpart 26 b of the embracing ring 26 and the upper end of the springreceiver 34. These springs 38 and 39 work as a suspension spring forsupporting the weight of the sprung member of the vehicle, and alsoexhibit the function of positioning the rod 31 of the fluid pressuredamper D to a neutral position relative to the cylinder 32, in which thespring 38 is juxtaposed to the fluid pressure damper D to energize thefluid pressure damper D in the extending direction, and the spring 39 isjuxtaposed to the actuator A to energize the fluid pressure damper D inthe contracting direction.

Since the upper ends of the springs 38 and 39 are supported by theembracing ring 26 connected to the mount 22, while the actuator A iselastically supported through the rubber vibration isolator 21 by themount 22, vibration of the springs 38 and 39 as the suspension spring isnot directly transmitted to the actuator A, and the vibration isolationto the suspension spring can be ensured.

The springs 38 and 39 also work to suppress transmission of vibration ofthe unsprung member of the vehicle toward the motor M side or to thesprung member, and also exert the effect of returning the rod 31 to theneutral position relative to the cylinder 32 of the fluid pressuredamper D. Since the rod 31 is returned to the neutral position relativeto the cylinder 32 by the springs 38 and 39 when the vibration of thesuspension device S is converged, the piston can be prevented from beingleft as it is located in the vicinity of the upper end or lower end tothe cylinder 32, and deterioration of vehicle ride quality ordeterioration of reliability of the suspension device S resulting froMinterference of the piston with the upper end or lower end of thecylinder 32 in subsequent input of vibration is never caused.

The neutral position referred to herein means a position where the rod31 is positioned relative to the cylinder 32 in a state where the sprungmember in the vehicle is supported by each spring 38, 39, but does notmean only a rod position where the piston connected to the end of therod 31 is located at the center of the cylinder 32.

In this case, since the function of positioning the rod 31 of the fluidpressure damper D to the neutral position can be consolidated to thesprings 38 and 39 as the suspension spring, it is not necessary toseparately provide a spring which performs only the positioning functionto the neutral position or performs only the suspension spring function,and the number of part items and the cost in the suspension device S canbe reduced. However, when the springs 38 and 39 are abolished, and thepositioning and returning of the rod 31 to the neutral position relativeto the cylinder 31 is performed by use of a suspension spring housedwithin each pressure chamber in the fluid pressure damper D or the like,the suspension spring may be separately provided, and the suspensionspring may be interposed indirectly between the mount 22 and theunsprung member by supporting the upper end of the suspension spring notonly by the mount 22 but also by the sprung member.

The positioning and returning of the rod 31 to the neutral positionrelative to the cylinder 32 may be performed by a means other than thesprings 38 and 39, for example, by folding the upper end of the covercylinder 37 inwardly so that a pair of cylinder-side spring receiversimmobile in the axial direction of the cylinder 32 is provided on theouter circumference of the cylinder 32 by the annular bottom of thecover cylinder 37 and the inwardly folded part at the upper end,disposing a rod-side spring receiver to be connected to the rod 31between the cylinder-side spring receivers, and interposing each springwhich energizes in the extending/contracting direction of the fluidpressure damper D each between the cylinder-side spring receivers andthe rod-side spring receiver, or in two positions.

In this suspension device S, when high frequency vibration such as avibration with relatively large acceleration, for example, is input tothe unsprung member in a case such that the vehicle travels along a badroad or runs on a projection on road, the fluid pressure damper D worksto absorb this vibration energy so that the vibration is hardlytransmitted to the threaded shaft 2 side, coupled with the vibrationtransmission suppressing effect by the springs 38 and 39, since it isserially connected to the threaded shaft 2 which is linearly moved bythe motor M.

The suspension device S of this embodiment adapted to convert avibration inputted from the unsprung member that is a linear motion intoa rotational motion includes many rotating members, and has propertiessuch that it tends to transmit the vibration of the unsprung member tothe sprung member because the moment of inertia to high frequencyvibration is large due to large inertial masses of the rotating members,coupled with the effect of friction between the spring receiver 34 andthe outer cylinder 27. However, as described above, the fluid pressuredamper D absorbs the vibration, and further the springs 38 and 39exhibit the vibration transmission suppressing effect, whereby thetransmission of the vibration to the threaded shaft 2 is suppressed.Therefore, this suspension device S never causes deterioration ofvehicle ride quality even in such a case.

Further, since direct action of high frequency vibration on the motor Mand the ball screw nut 1 is prevented by the fluid pressure damper D,transmission of high frequency vibration with particularly largeacceleration to the motor M and the ball screw nut 1 is suppressed.Thus, the reliability of the motor M and the ball screw nut 1 that areessential components of the suspension device S is improved, and thereliability of the suspension device S can be consequently improved.

Further, the spring receiver 34, which works as the bearing for theoverall extension/contraction of the suspension device S in slidablecontact with the inner circumference of the outer cylinder 27 asdescribed above, never presents a resistance to theextension/contraction of the fluid pressure damper D which absorbs highfrequency vibration, since it does not move in the vertical direction inFIG. 1 that is the axial direction relative to the outer cylinder 27 inresponse to extension/contraction of only the fluid pressure damper D.

That is, the spring receiver 34 which works as the bearing is inslidable contact with a position which does not affect theextension/contraction of the fluid pressure damper D to ensure smoothextension/contraction of the fluid pressure damper D. In this suspensiondevice S, therefore, the fluid pressure damper D is activelyextended/contracted, upon input of high frequency vibration, to absorbthe vibration, whereby the vibration insulation property to the sprungmember can be improved.

Further, in this embodiment, since the spring receiver 34 works as thebearing, it is not necessary to separately provide a bearing which worksonly as a bearing, and the number of part items can be reduced. When thespring receiver 34 is not caused to work as the bearing, and a bearingis separately provided, the bearing can be set between the outercylinder 27 and the cover cylinder 37 although it presents a resistanceto the expansion/contraction of the fluid pressure damper D.

In addition, since the spring receiver 34 which works as the bearingdoes not interfere with the extension/contraction of the fluid pressuredamper D upon input of high frequency vibration, direct action of impactforce on the actuator A is suppressed. Accordingly, the motor M and themotion conversion mechanism T can be protected to improve thereliability of the actuator A that is an essential component of thesuspension device S, and the reliability of the suspension device S canbe improved by dissolving the defect of the conventional suspensiondevice.

In this embodiment, since the actuator A is elastically supported by themount 22 connected to the sprung member through the rubber vibrationisolator 21, the vibration of the actuator A with large inertial weightcan be prevented from being directly transmitted to the sprung member,and since the actuator A is vibration-isolated from the springs 38 and39 as the suspension spring due to the presence of the rubber vibrationisolator 21, excitation of the sprung member by the inertia of theactuator A vibrating in the middle between the sprung member and theunsprung member can be also suppressed.

Further, by adopting the above-mentioned structure in which the actuatorA is elastically supported while being isolated from the springs 38 and39 as the suspension spring, even in a situation such that highfrequency vibration cannot be sufficiently absorbed by the fluidpressure damper D, and the actuator A difficult to extend/contract inresponse to input of high frequency vibration as described above reachesa so-called bar-like state, this vibration can be absorbed by the rubbervibration isolator 21 to break the transmission of the vibration to thesprung member.

Since the actuator A and the fluid pressure damper D are housed in theouter cylinder 27, the cover cylinder 37 and the mount 22 to isolate theessential drive part of the suspension device S from the outside of thesuspension device S in the suspension device S, penetration of rainwaterinto the suspension device S and contact of flying stones to theessential drive part can be surely prevented. Accordingly, thepracticability of the suspension device S is improved.

When the thus-constituted suspension device S is actually assembled, themotion conversion mechanism T and the fluid pressure damper D can beintegrated by inserting the connecting shaft 30 connected to the rod 31of the fluid pressure damper D into the disk 33 installed with thespring receiver 34 and the threaded shaft 2 of the assembly which iscomposed of only the motion conversion mechanism T retained by theholder 5, and screwing the nut 35 to the thread part 30 b at the upperend of the connecting shaft 30 from the upper end side in FIG. 1, andthe motor M is thereafter mounted on the upper end of the holder 5,whereby the assembling of the suspension device S is completed.

Since the motor M includes the cylindrical shaft 17 so as to insert thethreaded shaft 2 into the shaft 17, the shaft 17 of the motor M can beconnected to the ball screw nut 1 in the motion conversion mechanism Tfrom the side opposite to the fluid pressure damper after integratingthe motion conversion mechanism T to the fluid pressure damper D, andthe assembling process of the suspension device S is furtherfacilitated.

In this embodiment, the ball spline nut 3 to be engaged with the splinegroove provided in the outer circumference of the threaded shaft 2 isadopted as the locking mechanism since smooth vertical movement of thethreaded shaft 2 can be ensured. Otherwise, the locking mechanism can beretained by the holder 5 by simply forming a groove in the outercircumference of the threaded shaft 2 along its axial line, and fittinga member which does not inhibit the vertical movement of the threadedshaft 2 such as a key to the groove to lock the threaded shaft 2.

The scope of the present invention is never limited to those shown ordescribed in detail herein.

INDUSTRIAL APPLICABILITY

The suspension device of the present invention can be used for avehicular suspension.

1. A suspension device, comprising: an actuator including a motionconversion mechanism for converting rotational motion of a screw nut tolinear motion of a threaded shaft, and a motor connected to the screwnut; and a fluid pressure damper connected to the threaded shaft,wherein the threaded shaft is formed in a cylindrical shape, aconnecting shaft for connecting a rod or a cylinder of the fluidpressure damper to the threaded shaft is inserted into the threadedshaft, and the connecting shaft is connected to the threaded shaft fromthe side opposite to the fluid pressure damper.
 2. A suspension deviceaccording to claim 1, wherein the connecting shaft is detachablyconnected to the threaded shaft.
 3. A suspension device according toclaim 1, wherein the connecting shaft includes an engagement part to beengaged with a fluid pressure damper-side end of the threaded shaft, andthe connecting shaft is thread-fastened to a nut screwed to a leadingend thereof and the threaded shaft while engaging the engagement partwith the threaded shaft.
 4. A suspension device according to claim 1,further comprising a cylindrical spacer which is fitted to an end,opposite to the fluid pressure damper, of the threaded shaft to performcentering of the connecting shaft.
 5. A suspension device according toclaim 1, wherein the motor includes a cylindrical shaft, and thethreaded shaft is inserted into the shaft.
 6. A suspension deviceaccording to claim 2, wherein the connecting shaft includes anengagement part to be engaged with a fluid pressure damper-side end ofthe threaded shaft, and the connecting shaft is thread-fastened to a nutscrewed to a leading end thereof and the threaded shaft while engagingthe engagement part with the threaded shaft.
 7. A suspension deviceaccording to claim 2, further comprising a cylindrical spacer which isfitted to an end, opposite to the fluid pressure damper, of the threadedshaft to perform centering of the connecting shaft.
 8. A suspensiondevice according to claim 3, further comprising a cylindrical spacerwhich is fitted to an end, opposite to the fluid pressure damper, of thethreaded shaft to perform centering of the connecting shaft.
 9. Asuspension device according to claim 2, wherein the motor includes acylindrical shaft, and the threaded shaft is inserted into the shaft.10. A suspension device according to claim 3, wherein the motor includesa cylindrical shaft, and the threaded shaft is inserted into the shaft.11. A suspension device according to claim 4, wherein the motor includesa cylindrical shaft, and the threaded shaft is inserted into the shaft.